This invention relates to a shadow mask type cathode ray tube used for a television receiver, a computer display, and the like.
FIG. 18 is a cross-sectional view showing one example of a conventional color cathode ray tube. The color cathode ray tube 1 in FIG. 1 includes a substantially rectangular-shaped face panel 2 having a phosphor screen 2a formed on its inner surface, a funnel 3 connected to the rear side of the face panel 2, an electron gun 4 contained in a neck portion 3a of the funnel 3, a shadow mask 6 facing the phosphor screen 2a inside the face panel 2, and a mask frame 7 for fixing the shadow mask 6. Furthermore, in order to deflect and scan electron beams, a deflection yoke 5 is provided on the outer periphery of the funnel 3.
The shadow mask 6 plays the role of selecting colors with respect to three electron beams emitted from the electron gun 4. The shadow mask 6 is a flat plate in which a number of apertures, through which electron beams pass, are formed by etching. xe2x80x98Axe2x80x99 shows a track of the electron beams.
The frames 7 are plate members for fixing the shadow mask 6, and a pair of frames 8 to support the frames 7 are fixed to the longitudinal ends of the frames 7. The pair of frames 7 and the pair of frames 8 form a frame structure. This frame structure and a shadow mask 6 fixed to the frame structure compose a shadow mask structure 9.
Plate-shaped spring-attaching members 21 are adhered to the pair of top and bottom frames 7, and spring members 10 are fixed to these spring-attaching members 21. Plate-shaped spring-attaching members 11 are adhered to the pair of right and left frame 8, and spring members 12 are adhered to the spring-attaching members 11.
The shadow mask structure 9 is fixed to the face panel 2 by fitting attaching holes 10a of the spring members 10 with pins 13 provided to the top and bottom of the inner surface of the face panel 2, and by fitting the attaching holes 12a of the spring members 12 with pins (not shown) provided to the right and left of the inner surface of the face panel 2.
In a color cathode ray tube, due to the thermal expansion of the shadow mask 6 caused by the impact of the emitted electron beams, the apertures for passing electron beams are displaced. Consequently, a doming phenomenon occurs. That is, the electron beams passing through the apertures fail to hit a predetermined phosphor correctly, thus causing unevenness in colors. Therefore, a tensile force to absorb the thermal expansion due to the temperature rise of the shadow mask is applied in advance, and then the shadow mask 6 is stretched and held to the frames 7. When the shadow mask 6 is stretched and held as mentioned above, it is possible to reduce the displacement between an aperture of the shadow mask 6 and phosphor stripes of the phosphor screen 2a even if the temperature of the shadow mask 6 is raised.
However, the conventional color cathode ray tube described above suffered from the following problem. When an electron beam hits the stretched shadow mask 6, the shadow mask 6 is expanded by heat and reduces its tensile force. Thereby, the internal moment of the shadow mask structure 9 changes and the balance changes as well. Due to the change in the balanced state, a distance (q-value) between the apertures of the shadow mask 6 and the phosphor screen 2a is deviated, that is, the shadow mask 6 is displaced in the axial direction. This will prevent electron beams from hitting a desired position of the phosphor, which will lead to unevenness in colors.
Such color unevenness caused by the displacement of the shadow mask 6 in the axial direction cannot be prevented sufficiently even by stretching and holding the shadow mask as mentioned above.
It is an object of the present invention to provide a cathode ray tube that can solve the problems of conventional techniques. Such a cathode ray tube can suppress a shadow mask from being displaced in an axial direction and can prevent unevenness in colors.
To achieve the above object, a cathode ray tube of the present invention comprises a pair of plate members facing each other; a pair of supporters adhered to the respective plate members so as to support the plate members; and a shadow mask adhered to the respective plate members while being applied with a tensile force, and the supporters comprise crank-shaped steps formed to protrude toward the shadow mask. Since such a cathode ray tube can decrease an internal moment of the shadow mask structure, the displacement of the shadow mask in the axial direction can be suppressed and the q-value deviation also can be suppressed even if the shadow mask is expanded by heat generated by the impact of electron beams. Moreover, since the crank-shaped steps of the supporters serve to block a transverse gap with a ferrous material, the magnetic characteristics can be improved.
In the cathode ray tube, preferably, the supporters have portions extended from respective ends of the plate members in the longitudinal direction to the insides of the plate members, and the ends of the extended portions are adhered to the plate members so that the support members are adhered to the plate members at insides of the plate members in the longitudinal direction. Accordingly, the shadow mask will have a tensile force with a mountain-shaped distribution, so that vibration of the shadow mask can be suppressed easily at its free ends. Though the thermal expansion of the shadow mask will increase movement of the supporters, the stress is absorbed at parts insides of the plate members, and thus, stress applied to the axes of supporters to which the spring members are attached will be decreased. This provides further effects for decreasing an internal moment of the shadow mask structure.
Preferably, the supporters comprise spring-attaching members adhered to recesses at the crank-shaped steps so as to support the supporters, spring members are adhered to the spring-attaching members, attaching holes are formed in the spring members for accepting attaching pins, and the attaching holes have central points located opposing the shadow mask with respect to the supporters adhered to the plate members. A moment is applied to the support members due to the reaction force from shadow mask tensile force applied to the upper surfaces of the plate members. Since the above-mentioned cathode ray tube reduces the change in the moment, it can decrease the displacement of the upper surfaces of the plate members in the axial direction.
Preferably, the supporters comprise spring members adhered either at or outside the recesses at the crank-shaped steps so as to support the supporters, attaching holes are formed in the spring members for accepting attaching pins, and the attaching holes have central points located opposing the shadow mask with respect to the supporters adhered to the plate members. Such a cathode ray tube does not require any spring-attaching members since spring members are attached to the supporters directly.
Preferably, the crank-shaped steps have straight parts in the longitudinal direction of the supporters. In such a cathode ray tube, a member can be attached easily to the supporter, and the member is used for attaching a shadow mask structure comprising a shadow mask to a face panel.
Preferably, the crank-shaped steps have central axes at parts displaced toward the shadow mask, and the central axes are located above the shadow mask. Since the shadow mask gets closer to the phosphor screen due to thermal expansion of the shadow mask in such a cathode ray tube, unevenness in colors can be corrected.
Preferably, the crank-shaped steps have circular bent parts, and the inner radius of curvature at the circular bent parts is at least 20 mm. Such a cathode ray tube can prevent stress from being focused excessively at the bent parts, so that a sufficient rigidity can be maintained.
Preferably, support-adjusting members are adhered through the recesses at the crank-shaped steps, and the support-adjusting members are located facing the supporters. Such a cathode ray tube can not only decrease moment change but improve rigidity of the supporter. Since the cross-sectional second moment is increased, a rigid material used for the supporters can be decreased in size of the cross section. In addition, the displacement of the shadow mask in the axial direction can be suppressed further at a time of impact of emitted electron beams.
The supporter will have a cross-sectional second moment in the horizontal direction larger than a cross-sectional second moment about an axis in the axial direction. Therefore, the supporter is prevented substantially from being displaced in the axial direction while displacement in the horizontal direction is increased. Correction in the axial direction is available as well by using the horizontal displacement.
Preferably, the support-adjusting members comprise protrusions formed to lower spring constant of the support-adjusting members in the longitudinal direction. Accordingly, the support-adjusting member will relax the force in a direction for compressing the supporter at a time of operation of the cathode ray tube, and displacement of the shadow mask in the axial direction can be decreased.
Preferably, the spring constant of the support-adjusting members in the longitudinal direction is at most 1.47xc3x97104 N/mm.
Preferably, the support-adjusting members have a thermal expansion coefficient higher than that of the supporters. Accordingly, plastic deformation of the shadow mask can be prevented during heat treatment. Furthermore, displacement in the axial direction can be suppressed at a time of operation of the cathode ray tube.
Preferably, the support-adjusting members have a thermal expansion coefficient that is at least 1.2 times that of the supporters.
Preferably, support-adjusting members having a thermal expansion coefficient lower than a thermal expansion coefficient of the supporters are adhered to surfaces of the crank-shaped steps that are displaced toward the shadow mask. Such a cathode ray tube can prevent plastic deformation of the shadow mask during heat treatment.
Preferably, an internal magnetic shield is adhered to the support-adjusting members through an insulating material. Since such a cathode ray tube can suppress heat conduction from the supporters to the internal magnetic shield, and also suppress heat radiation effect of the internal magnetic shield, the supporters and the support-adjusting members can be kept stably at an identical temperature. Thereby, the movement amount of the electron beams can be stabilized and color displacement can be prevented.
Preferably, an internal magnetic shield is adhered to the support-adjusting members, and an area that the internal magnetic shield is contacted with the support-adjusting members is at most 25% of one surface of each of the support-adjusting members. Such a cathode ray tube in which the internal magnetic shield is contacted with the support-adjusting members at a small area can suppress thermal conduction from the supporters to the internal magnetic shield through the support-adjusting members, and also suppress heat radiation effect of the internal magnetic shield. Accordingly, the supporters and the support-adjusting members can be stabilized at the same temperature, and thus, the movement amount of the electron beams can be stabilized and color displacement can be prevented.
Preferably, the area that the internal magnetic shield is contacted with the support-adjusting members is at most 5% of one surface of each of the support-adjusting members. Such a cathode ray tube can suppress thermal conduction from the supporter to the internal magnetic shield through the support-adjusting members more reliably, so that color displacement can be prevented more certainly.
Preferably, an additional member is provided between the internal magnetic shield and the support-adjusting members, and the additional member has a thermal conductivity that is lower than that of the internal magnetic shield or of the support-adjusting members. Such a cathode ray tube can suppress thermal conduction from the supporters to the internal magnetic shield through the support-adjusting members with more certainty.
Preferably, the material of the additional member having a low thermal conductivity is SUS 304.
Preferably, the internal magnetic shield is connected with the support-adjusting members through a protrusion formed in at least either the internal magnetic shield or the support-adjusting members, and the contact area is equal to the connection area at the protrusion. Such a cathode ray tube can decrease the contact area between the internal magnetic shield and the support-adjusting members while connecting the internal magnetic shield and the support-adjusting members more easily and certainly.